s3s-fs: check path

use s3s::s3_error;

use s3s::S3Result;

use s3s::S3;

use tokio::io::BufWriter;

use std::collections::VecDeque;

use std::io;

use tokio::fs;

use tokio::io::AsyncSeekExt;

use tokio::io::BufWriter;

use tokio_util::io::ReaderStream;

use futures::TryStreamExt;

        let src_path = self.get_object_path(bucket, key)?;

        let dst_path = self.get_object_path(&input.bucket, &input.key)?;

        if src_path.exists().not() {

            return Err(s3_error!(NoSuchKey));

        }

        let file_metadata = try_!(fs::metadata(&src_path).await);

        let last_modified = Timestamp::from(try_!(file_metadata.modified()));

    async fn list_objects_v2(&self, input: ListObjectsV2Request) -> S3Result<ListObjectsV2Output> {

        let path = self.get_bucket_path(&input.bucket)?;

        if path.exists().not() {

            return Err(s3_error!(NoSuchBucket));

        }

        let mut objects: Vec<Object> = Default::default();

        let mut dir_queue: VecDeque<PathBuf> = Default::default();

        dir_queue.push_back(path.clone());